The use of synthetic fibers has increased in many areas of technology. Among those areas which have had a very great and varied increase is carpets, area rugs, carpeting and all types of floor covering. The teachings and publications in this and related fields are quite extensive and describe details for separating, reconstituting, recovering, purifying and variously treating and handling used textiles and carpeting and include natural and synthetic fibers in the processing and recovery steps.
More specifically, U.S. Pat. No. 3,006,867 (Simon) discloses a method of reconstituting a synthetic plastic, such as and including nylon from waste and used materials and include textile wastes having nylon fibers. The method consists of dissolving the waste material from the synthetic plastic in formic acid, mixing a hydrocarbon selected from n-hexane, cyclohexene, n-heptane, cyclohexane, hexene, benzene, and toluene with the formic acid-plastic solution in an amount sufficient to form an azeotropic mixture, then heating the azeotropic mixture to a temperature sufficient to vaporize the azeotropic mixture and removing (recovering) the vapors from the distillation zone to leave behind the desired synthetic plastic being recovered.
U.S. Pat. Nos. 4,003,880; 4,003,881; 4,118,187 and 4,137,393 (Sidebotham et al.) variously disclose methods for recovering polyester from dyed polyester fibers as in fabrics, textiles, carpeting and commercial products. Only polyesters are involved in the recovery steps. While the conditions and procedural steps vary in the patent disclosures, there are certain steps which are disclosed in and utilized in all these patent processes. These steps generally include:
1) Contacting collections of yarns, fibers, and fabrics, including dyed polyester fibers with a dye-stripping solvent for polyester polymer, which is preferably not a solvent for the remaining constituents, at a temperature below which the polyester fiber dissolves and above the temperature where the crystal lattice of the polyester fibers swell so as to release the dye, thereby stripping the dye from the polyester fibers; PA0 2) Removing the excess of the dye-containing, dye-stripping solvent which is not absorbed by the fibers and fabrics; PA0 3) Contacting the fibers (which may contain residual dye-stripping solvent) with a sufficient addition of a primary dissolution solvent under selective dissolution conditions for polyester fibers; PA0 4) Removing the undissolved fibers or the other impurities from the solution; and PA0 5) Separating the solvent or solvents from the polyester by evaporating the solvent from the dissolved and/or molten polyester without precipitating the polyester from the solution.
It is significant and important to point out that none of these recovery methods disclose or suggest any steps or detailed recovery procedures for nylon. Rather, they are limited to specific dissolution techniques for recovery of the unrelated polymer, polyester. In another U.S. Pat. No. 4,064,079 (Sidebotham et al.) a modified polyester recovery method is disclosed which does not include a step for removal of dye from the polyester fibers.
U.S. Pat. Nos. 5,240,530 and 5,288,349 (Fink) teach a carpet recycling and recovery method in which portions of the carpet are initially ground and melted for a feedstock. Carpets containing different types of materials are ground mechanically so that the contained fiber length is reduced between 1/4" and 1/16". These fibers are then separated in an aqueous bath on the basis of specific gravity. Neither of these patents teach or suggest separating nylon fibers from polyester fibers by subjecting the mixed fibers to water and then heat, that is, there are no extraction steps disclosed.
U.S. Pat. No. 5,294,384 (David et al.) discloses a method for converting waste carpet material into a thermoplastic composition. As starting material, the carpet samples (waste) may have any pile weight and also may be comprised of non-homogenous mixtures of components. The samples are melt blended with or without a compatibilizer in a temperature range of from 250 degrees Celsius to 260 degree Celsius and at a pressure of from about 350 to 450 psi and a shear rate of about 200-400/sec.; most preferably this step is carried out in a twin screw extruder. The blends thus formed may then be pelletized or processed into other commercially acceptably forms. Blend compositions which are disclosed include mixtures of nylon, polyolefins, SBR latex, and inorganic fiber. Using the method described in this patent, no attempt is made (no steps included) to separate the fiber mixture into their constituent parts or fractions; rather, the mixtures are merely transformed into a different mixture having a different form from the starting components.
In U.S. Pat. No. 5,370,747 (Corbin et al.) a carpet product is disclosed which has two distinct sections, a top section constructed entirely from nylon (Nylon 6) and a bottom section. The top section is thus easily removable from the bottom section for replacement thereof without any damage to the bottom section. After such removal, the top section can then be recycled to e-Caprolactrum for re-use in Nylon 6 carpet or it can be used in other Nylon-6 products.
Further, U.S. Pat. No. 5,342,854 (Serod) describes a method for separating and recovering polyester from polyester/cotton blends. The polyester/cotton material is cut and chopped into small pieces and then dried. These dried scraps are placed into a vessel containing a sulfone solvent such as an alkyl sulfone having from 1 to 10 carbon atoms and heated to 150 degrees Celsius. The mixture is steeped (with agitation) for about 90 minutes at this temperature. Thereafter, the temperature of the mixture is raised to 190 degrees Celsius and maintained thus for about another 35 minutes. The solvent containing polyester is then separated for further treatment to precipitate the recovered polyester. There are no methods or steps described for separating the polyester from any other polymeric systems or other polymeric fibers.
U.S. Pat. No. 5,198,471 does not teach a process related to this invention. There is no disclosure of nylon fibers, carpet, or any of the solvents. In U.S. Pat. No. 3,696,058 (Tate) a process is disclosed for recovering solid scrap thermoplastic polymers such as polyamides and polyesters. The process comprises the following steps:
(a) dissolving said thermopolastic polymer in hexafluorisopropanol, PA1 (b) filtering said polymer solution PA1 (c) mixing the polymer solution with an excess of water at a temperature of from 60 to 100 degrees Celsius, and PA1 (d) separating the precipitated polymer from the water, wherein the thermoplastic polymer is selected from the group consisting of polyamide, polyester, polyacrylonitrile and polyacetal.
In this patent the solvents employed for the polymer are fluoroalcohols. It has been known to use formic acid and sulfuric acid as well as various types of solvents such as for instance ethylene glycol, propylene glycol, meta-cresol and various triglycerides and fatty acids to dissolve nylon polymeric materials as a step in producing cast polyamide fibers including nylon fibers.